I. Field
The present invention generally relates to communications, and more particularly, to handoff of data attachment points in wireless communication systems.
II. Background
In telecommunications, especially wireless communications, communication environments are not static but rather dynamic. In a mobile communication setting, some communication entities such as an Access Terminal (AT) may move from one location to another at different points in time.
Reference is directed to FIG. 1 which shows a simplified schematic illustrating an exemplary communication system. In the following description, terminology associated with a Ultra Mobile Broadband (UMB) system is used. The basic terminology and principles of operations of the UMB system can be found from a publication by the 3rd Generation Partnership Project 2 (3GPP2) established by the Telecommunication Industry Association (TIA), entitled “Interoperability Specification,” 3GPP2-A.S0020. As shown in FIG. 1, within the Radio Access Network (RAN) 12, for example, in a Ultra Mobile Broadband (UMB) system in which an AT 14 is accessing a backbone network 16 via an evolved Base Station (eBS) 18 wirelessly. The eBS 18 serves as a data exchange entity between the AT 14 and an Access Gateway (AGW) 20. The AGW 20 has direct access to the backbone network 16. The backbone network 16 can be the Internet, for instance.
In FIG. 1, the eBS 18 serves as the Data Attachment Point (DAP) for the AT 14. More specifically, the eBS 18 serving as the DAP has the forward link traffic binding with the AGW 20, for example, as operated under the Proxy Mobile IP (PMIP) protocol promulgated by the Internet Engineering Task Force (IETF). Under the PMIP protocol, the AGW 20 sends forward-link data traffic to the DAP, the eBS 18 in this case, which in turn directs the data traffic to the AT 14. The eBS 18, acting as the DAP, is the network entity which performs the last binding with the AGW 20.
In a wireless environment, the AT 14 is mobile. That is, the AT 14 may move from one location to another, within the same RAN 12 or to a different RAN.
Reference is now directed to FIG. 2 which shows another simplified schematic illustrating the mobility of the AT 14.
Suppose in FIG. 2, the AT 14 originally communicating with eBS 18 now moves away from eBS 18 and begins to communicate with the eBS 22. The eBS 22 is now called the Forward-Link Serving eBS (FLSE) for the AT 14 as it is the eBS 22 that directly communicates and exchanges data with the AT 14. However, there has not been any binding update with the AGW 20. That is, the network entity that performed the last binding with the AGW 20 was still the eBS 18 and there has not been any binding update with the AGW 20 since then. As such, the eBS 18 still serves as the DAP. Under such a scenario, data from the AGW 20 is sent to the eBS 18 which is the DAP in this case, and then routed to the AT 14 to the eBS 20 which serves as the FLSE. Data packets from the AGW 20 to the AT 14 are routed according to the data path 24 as shown in FIG. 2.
Even though the AT 14 has roamed away from the coverage area served by the eBS 18, the eBS 18 remains the DAP for the AT 14. The reason is in a wireless setting, depending on the mobility of the AT 14, it is possible that the eBS 18 may again become the FLSE for the AT 14. For instance, the AT 14 may be on the boundary line of the coverage areas provided by both the eBS 18 and the eBS 22. Consequently, the AT 14 may only communicate with the eBS 22 temporarily. However, if the communications between the AT 14 and the eBS 22 are not temporary, routing data packets via the meandering data path 24 may not be an efficient usage of communication resources, at least from the perspective of backhaul utilization. In addition, packet data latency is also impacted. Instead, the DAP is preferably switched from the eBS 18 to the eBS 22. For such a DAP switch, the eBS 22 needs first to perform a forward link traffic binding with the AGW 20. After the successful completion of the forward link traffic binding process, the eBS 22 becomes the current DAP. Data packets are then routed from the AGW 20 to the AT 14 via the eBS 22, as shown by the data path 26 in FIG. 2. The switch of DAP from BS 18 to eBS 22 can be based on certain criteria, for example, after it is assured that the AT communicates with eBS 22 for a predetermined period of time.
Heretofore, switching or selection of the DAP, called a DAP handoff, has mostly been AN-initiated. In the AN-initiated handoff, the handoff process is transparent to the AT 14. However, problems may arise if the AN 14 has no knowledge of the handoff. For instance, the intended DAP may turn out to be the non-intended DAP. This is especially true in a asynchronous environment in which the various communication entities are not synchronized with each other. Referring back to FIG. 2, again suppose the AT 14 is at the boundary of the coverage areas of both eBS 18 and eBS 22. Sensing the presence of the AT 14, e.g., via the downlink signal strength, in an AN-initiated handoff, both the eBS 18 and the eBS 22 attempt to be the DAP by registering with the AGW 20 for the forward-link binding. Further suppose that the AT 14 is well settled within the coverage area provided by the eBS 18, and consequently the eBS 18 should be the most suitable DAP for the AT 14. Nevertheless, if registration messages sent and received between the AGW 20 and the eBS 22 are faster than those between the AGW 20 and the eBS 18, the eBS 22 can be assigned as the DAP ahead of the eBS 18, contrary to what was intended. Recovery of the wrongly assigned DAP, even if not fatal to the communication session involved, requires additional signaling and messaging which unnecessarily tie up communication resources.
Accordingly, there is a need to provide a DAP assignment scheme with more accuracy and certainty, thereby allowing more efficient utilization of communication resources.